Communication apparatus and communication method

ABSTRACT

To improve throughput by reducing the resource used for transmitting a parameter relating to retransmission control and decreasing overhead of retransmission control signaling. Where a retransmission control method is employed with adaptive MCS control in which the encoding rate can be changed, the scheduling section sets the MCS in accordance with CQI notified from the communication counterpart apparatus. When transmission data is encoded, the RV parameter bit-number setting section sets the number of bits used for signaling the RV parameter to decrease as the encoding rate of the first transmission is decreased and sets the RV parameter based on the number of bits. For example, in a case where the encoding rate R is R&gt;2/3, two bits are set. In a case where the encoding rate 1/3&lt;R≦2/3, one bit is set. On the other hand, in a case where R≦1/3, zero bits is set.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 13/933,892filed Jul. 2, 2013, which is a continuation application of applicationSer. No. 12/920,447 filed Aug. 31, 2010, which is a 371 application ofPCT/JP2009/001078 filed Mar. 10, 2009, which is based on JapaneseApplication No. 2008-062,680 filed Mar. 12, 2008, the entire contents ofeach of which are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a wireless communication apparatus thatcan be applied to a wireless communication system such as a cellularsystem, and more particularly, to a wireless communication apparatus, awireless communication system, and a wireless communication method thathave a retransmission control function.

BACKGROUND ART

Recently, in wireless communication, a retransmission control methodthat combines propagation path encoding and retransmission compositionhas called attention as a system implementing high-speed transmission byeffectively using the limited frequency band. As a combination of thepropagation path encoding and the retransmission composition in aretransmission control method, a combination of a turbo code for which aflexible encoding rate can be set with puncture and an IR (incrementalredundancy) method in which a punctured parity bit is slightly addedeach time when a retransmission occurs is effective. Such aretransmission control method is precisely referred to as Hybrid ARQ(HARQ). However, hereinafter, such a retransmission control method isdescribed simply as “retransmission control”.

In Non Patent Citation 1, as an error correction method using adaptivefeedback, technology for improving the error correction capability byusing the IR is disclosed. In addition, in 3GPP-LTE (3rd GenerationPartnership Project Long Term Evolution) that is a specification of thenext cellular system, in order to simplify the definition ofretransmission data such as the redundancy version (hereinafter,referred to as RV), CBRM (Circular Buffer based Rate-Matching) isreviewed (see Non Patent Citation 2). The CBRM is a rate matching methodin which the RV is defined by sequentially reading out a turbo codeaccumulated in a circular buffer that is a sequential read-type bufferfrom any arbitrary start position in order of the buffer address.

An example of the operation of the retransmission control that combinespropagation path coding and the retransmission composition will bebriefly described with reference to FIG. 15. FIG. 15 is a diagramrepresenting a concrete example of the relationship between transmissiondata and RV parameter settings in the retransmission control and showsthe image of an IR buffer in a case where the encoding rate R=5/6. Inthe retransmission control using the IR, an RV parameter that representsthe start position of the retransmission data for retransmission is set.Thus, on the transmission side, the data from the start position that isdesignated by the RV parameter is transmitted as the retransmissiondata, and the receiver side and the reception side is notified of thisRV parameter.

When the transmission data is generated on the transmission side, turboencoding is performed for systematic bits (denoted by S in the figure)in which information to be transmitted is included so as to generateparity bits (in the figure, denoted by P), and the encoded data isstored in the IR buffer. A puncture process is performed for the paritybits of the encoded data inside the IR buffer with a uniform rule, and apart of the encoded data is extracted and transmitted. At the firsttransmission, the left end in the figure inside the IR buffer is set asthe data start position.

FIG. 15 represents a configuration example in which an RV parameter isrepresented by 2 bits, and a total of four data start positions (in thefigure, denoted by white circles) are arranged. In such a case, at thefirst transmission, RV=0, a part of the systematic bits S and the paritybits P is transmitted from the start position by using all the number ofbits that can be transmitted by using predetermined physical resources.Here, the remaining data out of the encoded data inside the IR buffer ishandled as untransmitted data. When an Nack signal is fed back from thereception side, and retransmission is to be performed, RV is set as RV=2as the second transmission data, and data inside the IR buffer isextracted from the third start position from the left side, and a signalis transmitted by using the same number of bits as that of the firsttransmission. Thereafter, at the third transmission, RV is set as RV=1,at the fourth transmission RV is set as RV=3, and as shown in FIG. 15,data inside the IR buffer is extracted from a respective start positionand is transmitted.

In a wireless communication system such as a cellular system, adaptiveMCS (Modulation and Coding Scheme) control in which a modulation typeand an encoding rate are adaptively changed in accordance with thereception quality is reviewed. In the adaptive MCS control, the encodingrate is changed by puncture or repetition of a bit row after encoding.

-   [Non Patent Citation 1] David M. Mandelbaun, “An adaptive-feedback    coding scheme using incremental redundancy”, Information Theory,    IEEE Transactions on, May 1974, P. 388-389-   [Non Patent Citation 2] R1-072604, “Way forward on HARQ rate    matching for LTE”, Ericsson, et al., 3GPP TSG-RAN WG1 RAN1#49,    2007/05

SUMMARY Technical Problem

By introducing the adaptive MCS control or retransmission control, anadvantage of improving the throughput can be acquired by flexiblysetting parameters in accordance with the state of the propagation path.However, in retransmission control signaling for applying the adaptiveMCS control, data having a high encoding rate is effectively used, andan RV parameter needs to be set so as to represent a plurality of datatime points. Accordingly, there is a problem that the RV parametersetting cannot effectively used for data having a low encoding rate.

FIG. 16 is diagram representing a concrete example of the relationshipbetween transmission data and RV parameter setting in the retransmissioncontrol in a case where the encoding rate is changed. (a) is an IRbuffer image for a case where the encoding rate R=5/6, and (b) is an IRbuffer image for a case where the encoding rate R=1/4.

As in FIG. 16( a), in a case where the encoding rate is high as R=5/6,in order to effectively utilize a parity bit that is untransmitted atthe first transmission through the puncture process, RV parametersetting of about two bits is necessary. On the other hand, as shown inFIG. 16( b), in a case where the encoding rate is low as R=1/4,repetition of the parity bit is performed at the first transmission, andall encoded data is transmitted. Accordingly, when the RV parametersetting for a high encoding rate is directly applied to data having alow encoding rate, the same data is repeatedly transmitted withoutdepending on the arranged two bits of the RV parameter. Therefore, thesituation is the same as setting RV=0 every time. Accordingly, theresource of the RV parameter is useless, and there is a problem in thatthe throughput decreases.

The present invention is contrived in consideration of theabove-described situations. The object of the present invention is toprovide a wireless communication apparatus, a wireless communicationsystem, and a wireless communication method capable of improving thethroughput by reducing the resource used for transmission of a parameterrelating to the retransmission control and decreasing the signalingoverhead for retransmission control.

Technical Solution

According to a first aspect of the present invention, there is provideda wireless communication apparatus including: a propagation path qualityacquiring section that receives a measurement result of a propagationpath quality from a communication counterpart apparatus; an MCS settingsection that sets an MCS (Modulation and Coding Scheme) including anencoding rate in accordance with the measurement result of thepropagation path quality; an encoding section that encodes transmissiondata in accordance with the MCS; a retransmission control section thatcontrols retransmission of transmitted data based on a response signaltransmitted from the communication counterpart apparatus; a parameterbit-number setting section that sets the number of bits of aretransmission control parameter in accordance with the encoding rate ofa first transmission so as to decrease the number of bits of theretransmission control parameter as the encoding rate is smaller; aretransmission control parameter setting section that sets theretransmission control parameter by using the set number of bits; acontrol signal generating section that generates a control signal havingcontrol information including the MCS and the retransmission controlparameter; and a transmission processing section that transmits to thecommunication counterpart apparatus the control signal and the encodeddata.

Accordingly, in a case where the encoding rate is low, and thegranularity of control of the retransmission control parameter isallowed to be rough, by decreasing the number of bits of theretransmission control parameter, the resource used for transmitting theparameter relating to the retransmission control can be reduced.Therefore, the throughput can be improved by decreasing the overhead ofretransmission control signaling.

According to a second aspect of the present invention, there is providedthe above-described wireless communication apparatus, wherein theparameter bit-number setting section, in a case where the encoding rateof the first transmission is equal to or lower than a predeterminedvalue, sets the number of bits of the retransmission control parameterto be smaller than that in a case where the encoding rate is equal to orhigher than the predetermined value.

According to a third aspect of the present invention, there is providedthe above-described wireless communication apparatus, wherein theparameter bit-number setting section sets the number of bits of theretransmission control parameter to zero bits in a case where theencoding rate of the first transmission is equal to or lower than apredetermined value.

According to a fourth aspect of the present invention, there is providedthe above-described wireless communication apparatus, wherein thewireless communication apparatus performs communication by using aplurality of code words, wherein the MCS setting section sets the MCSfor each of the plurality of code words, and wherein the parameterbit-number setting section sets the number of the bits of theretransmission control parameter to be smaller for the code word havinga smaller encoding rate of the first transmission out of the pluralityof code words.

Accordingly, while retransmission control can be flexibly set for a codeword that has a high encoding rate of the first transmission and hasmuch untransmitted data, the resource used for transmission of theretransmission control parameter can be reduced for a code word that isnot influenced much by decreasing the degree of freedom of theretransmission control parameter. Therefore, the throughput can beimproved by decreasing the overhead of retransmission control signalingfor a plurality of code words.

According to a fifth aspect of the present invention, there is providedthe above-described wireless communication apparatus, wherein theparameter bit-number setting section, while maintaining a total numberof bits of the retransmission control parameters to be constant, adjuststhe numbers of bits between the plurality of code words and sets thenumber of bits of the code word having a lower encoding rate of thefirst transmission to be smaller.

According to a sixth aspect of the present invention, there is providedthe above-described wireless communication apparatus, wherein theparameter bit-number setting section sets the number of bits of the codeword having the encoding rate of the first transmission that is equal toor lower than a predetermined value to zero bits.

According to a seventh aspect of the present invention, there isprovided the above-described wireless communication apparatus, whereinthe wireless communication apparatus performs communication by using aplurality of streams for a plurality of code words. In addition, thewireless communication apparatus further includes a stream-numbersetting section that sets the number of streams for each of theplurality of code words, wherein the parameter bit-number settingsection sets the number of bits of the retransmission control parameterto be smaller for the code word having a smaller number of streams ofthe first transmission out of the plurality of code words.

Accordingly, while the retransmission control can be flexibly set for acode word having the number of streams of the first transmission to behigh, the resource used for transmitting the retransmission controlparameter can be reduced for a code word that may transmit theuntransmitted data much more with high possibility by increasing thenumber of streams at the time of retransmission. Therefore, thethroughput can be improved by decreasing the overhead of retransmissioncontrol signaling for a plurality of code words.

According to an eighth aspect of the present invention, there isprovided the above-described wireless communication apparatus, whereinthe parameter bit-number setting section, while maintaining a totalnumber of bits of the retransmission control parameter to be constant,adjusts the numbers of bits between the plurality of code words and setsthe number of bits of the code word having a smaller number of streamsof the first transmission to be smaller.

According to a ninth aspect of the present invention, there is providedthe above-described wireless communication apparatus, wherein theparameter bit-number setting section sets the number of bits of the codeword having the number of streams of the first transmission equal to orsmaller than a predetermined value to zero bits.

According to a tenth aspect of the present invention, there is provideda wireless communication apparatus including: a propagation path qualitynotifying section that measures a propagation path quality between acommunication counterpart apparatus and the wireless communicationapparatus and notifies of a measurement result of the propagation pathquality; a reception processing section that receives a control signaland data from the communication counterpart apparatus; a controlinformation storing section that acquires an MCS including an encodingrate from control information included in the control signal and storesinformation on the encoding rate of a first transmission; aretransmission control parameter demodulating section that identifiesthe number of bits of a retransmission control parameter that is set inaccordance with the encoding rate of the first transmission anddemodulates the retransmission control parameter included in the controlinformation; and a decoding section that decodes received data based onthe retransmission control parameter.

Accordingly, by decreasing the number of bits of the retransmissioncontrol parameter in a case where the encoding rate is low, the resourceused for transmitting the parameter relating to the retransmissioncontrol can be reduced, and the overhead of retransmission controlsignaling can be decreased. Therefore, the throughput can be improved.On the reception side, the retransmission control parameter can beaccurately identified, and decoding or the like can be performed at thetime of retransmission.

According to an eleventh aspect of the present invention, there isprovided the above-described wireless communication apparatus, whereinthe wireless communication apparatus performs communication by using aplurality of code words, wherein the control information storing sectionstores control information for each of the plurality of code words, andwherein the retransmission control parameter demodulation sectionidentifies the number of bits of the retransmission control parameterthat is set in accordance with the encoding rate of the firsttransmission from the plurality of code words and demodulates theretransmission control parameter.

Accordingly, for a code word that has a low encoding rate and is notinfluenced much by decreasing the degree of freedom of theretransmission control parameter, the resource used for transmitting theretransmission control parameter can be reduced, and the overhead ofretransmission control signaling for a plurality of code words can bedecreased. Therefore, the throughput can be improved. On the receptionside, the retransmission control parameter can be accurately identified,and decoding or the like can be performed at the time of retransmissionof each code word.

According to a twelfth aspect of the present invention, there isprovided the above-described wireless communication apparatus, whereinthe wireless communication apparatus performs communication by using aplurality of streams for a plurality of code words, wherein the controlinformation storing section stores control information for each of theplurality of code words, and wherein the retransmission controlparameter demodulating section identifies the number of bits of theretransmission control parameter set in accordance with the number ofstreams of the first transmission from the plurality of code words anddemodulates the retransmission control parameter.

Accordingly, for a code word that has a small number of streams of thefirst transmission and may transmit untransmitted data much more withhigh possibility by increasing the number of streams at the time ofretransmission, the resource used for transmitting the retransmissioncontrol parameter can be reduced, and the overhead of retransmissioncontrol signaling of a plurality of code words can be decreased.Therefore, the throughput can be improved. On the reception side, theretransmission control parameter can be accurately identified, anddecoding or the like can be performed for each code word at the time ofretransmission.

According to a thirteenth aspect of the present invention, there isprovided a wireless communication base station apparatus including anyof the above-described the wireless communication apparatus.

According to a fourteenth aspect of the present invention, there isprovided a wireless communication mobile station apparatus including anyof the above described the wireless communication apparatus.

According to a fifteenth aspect of the present invention, there isprovided a wireless communication system including: a transmissionapparatus including a propagation path quality acquiring section thatreceives a measurement result of a propagation path quality from areceiver apparatus as a communication counterpart apparatus, an MCSsetting section that sets an MCS including an encoding rate inaccordance with the measurement result of the propagation path quality,an encoding section that encodes transmission data in accordance withthe MCS, a retransmission control section that controls retransmissionof transmitted data based on a response signal transmitted from thereceiver apparatus, a parameter bit-number setting section that sets thenumber of bits of a retransmission control parameter in accordance withthe encoding rate of a first transmission to so as to decrease thenumber of bits as the encoding rate is smaller, a retransmission controlparameter setting section that sets the retransmission control parameterby using the set number of bits, a control signal generating sectionthat generates a control signal having control information including theMCS and the retransmission control parameter, and a transmissionprocessing section that transmits to the receiver apparatus the controlsignal and the encoded data; and the receiver apparatus including apropagation path quality notifying section that measures the propagationpath quality between the transmission apparatus and the wirelesscommunication apparatus and notifies of the measurement result of thepropagation path quality, a reception processing section that receivesthe control signal and the data from the transmission apparatus, acontrol information storing section that acquires an MCS including anencoding rate from the control information included in the controlsignal and stores information on the encoding rate of the firsttransmission, a retransmission control parameter demodulating sectionthat identifies the number of bits of the retransmission controlparameter that is set in accordance with the encoding rate of the firsttransmission and demodulates the retransmission control parameterincluded in the control information, and a decoding section that decodesreceived data based on the retransmission control parameter.

According to a sixteenth aspect of the present invention, there isprovided a wireless communication method including: receiving ameasurement result of a propagation path quality from a communicationcounterpart apparatus; setting an MCS including an encoding rate inaccordance with the measurement result of the propagation path quality;encoding transmission data in accordance with the MCS; controllingretransmission of transmitted data based on a response signaltransmitted from the communication counterpart apparatus; setting thenumber of bits of a retransmission control parameter in accordance withthe encoding rate of a first transmission so as to decrease the numberof bits as the encoding rate is smaller; setting the retransmissioncontrol parameter by using the set number of bits; generating a controlsignal having control information including the MCS and theretransmission control parameter; and transmitting to the communicationcounterpart apparatus the control signal and the encoded data.

According to a seventeenth aspect of the present invention, there isprovided a wireless communication method including: measuring apropagation path quality between a communication counterpart apparatusand the wireless communication apparatus and notifying of a measurementresult of the propagation path quality; receiving a control signal anddata from the communication counterpart apparatus; acquiring an MCSincluding an encoding rate from control information included in thecontrol signal and storing information on the encoding rate of a firsttransmission; identifying the number of bits of a retransmission controlparameter that is set in accordance with the encoding rate of the firsttransmission and demodulating the retransmission control parameterincluded in the control information; and decoding received data based onthe retransmission control parameter.

Advantageous Effects

According to the present invention, there are provided a wirelesscommunication apparatus, a wireless communication system, and a wirelesscommunication method capable of improving the throughput by reducing theresource used for transmitting a retransmission control parameter anddecreasing the overhead of retransmission control signaling.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically representing signal transmission in acommunication system according to an embodiment of the presentinvention.

FIG. 2 is a diagram schematically representing a setting example of theRV parameter according to a first embodiment of the present invention.

FIG. 3 is a block diagram representing the configuration of the majorpart of the transmission apparatus used in the first embodiment of thepresent invention.

FIG. 4 is a block diagram representing the configuration of the majorpart of the receiver apparatus used in the first embodiment of thepresent invention.

FIG. 5 is a sequence diagram representing a concrete example of thesequence of all the processes relating to the communication between thetransmission apparatus and the receiver apparatus according to the firstembodiment.

FIG. 6 is a diagram representing an example of setting the number ofbits of a RV parameter corresponding to an encoding rate, according tothe first embodiment.

FIG. 7 is a diagram representing an example of setting the RV parameteraccording to the first embodiment.

FIG. 8 is a diagram schematically representing a setting example of theRV parameter according to a second embodiment of the present invention.

FIG. 9 is a block diagram representing the configuration of the majorpart of the transmission apparatus used in the second embodiment of thepresent invention.

FIG. 10 is a block diagram representing the configuration of the majorpart of the receiver apparatus used in the second embodiment of thepresent invention.

FIG. 11 is a diagram representing examples of setting the number of bitsof the RV parameter according to a decoding rate, according to thesecond embodiment.

FIG. 12 is a diagram schematically representing a setting example of theRV is parameter according to a third embodiment of the presentinvention.

FIG. 13 is a block diagram representing the configuration of the majorpart of a transmission apparatus used in the third embodiment of thepresent invention.

FIG. 14 is a block diagram representing the configuration of the majorpart of a receiver apparatus used in the third embodiment of the presentinvention.

FIG. 15 is a diagram representing a concrete example of the relationshipbetween transmission data and RV parameter settings in retransmissioncontrol.

FIG. 16 is diagram representing a concrete example of the relationshipbetween transmission data and RV parameter setting in the retransmissioncontrol in a case where the encoding rate is changed.

EXPLANATION OF REFERENCE CHARACTERS

-   -   101: WIRELESS BASE STATION    -   102: USER EQUIPMENT    -   311, 911: ENCODING UNIT    -   312, 912: RATE MATCHING UNIT    -   313: RV PARAMETER BIT-NUMBER SETTING UNIT    -   314, 914: CONTROL SIGNAL GENERATING UNIT    -   315: MULTIPLEXING UNIT    -   316, 916 a, 916 b: TRANSMISSION RF UNIT    -   317, 917 a, 916 b: ANTENNA    -   318, 918: RECEPTION RF UNIT    -   319, 919: SEPARATION UNIT    -   320, 920: DEMODULATING AND DECODING UNIT    -   321, 921: CRC TEST UNIT    -   322, 922: Ack/Nack SIGNAL ADJUSTING UNIT    -   323, 923: CQI DEMODULATING UNIT    -   324, 924, 1301: SCHEDULING UNIT    -   431, 1031 a, 1031 b: ANTENNA    -   432, 1032 a, 1032 b: RECEPTION RF UNIT    -   433, 1033: CHANNEL ESTIMATING UNIT    -   434, 1034: CONTROL SIGNAL DEMODULATING UNIT    -   435: DEMODULATING UNIT    -   436, 1036: DECODING UNIT    -   437, 1037, 1401: RV PARAMETER IDENTIFYING UNIT    -   438, 1038: FIRST-RIME MCS CONSERVATION UNIT    -   439, 1039: LIKELIHOOD CONSERVATION UNIT    -   440, 1040: CRC TEST UNIT    -   441, 1041: SINR MEASURING UNIT    -   442, 1042: FEEDBACK INFORMATION GENERATING UNIT    -   443, 1043: Ack/Nack GENERATING UNIT    -   444, 1045: ENCODING UNIT    -   445, 1045: MULTIPLEXING UNIT    -   446, 1046: TRANSMISSION RF UNIT    -   913, 1302: INTER-CODE WORD RV PARAMETER BIT-NUMBER ADJUSTING        UNIT    -   915: MIMO MULTIPLEXING UNIT    -   925, 1303: RV PARAMETER BIT-NUMBER CONSERVATION UNIT FOR EACH        CODE WORD    -   1035: MIMO DEMODULATING UNIT    -   1402: FIRST-TIME STREAM-NUMBER CONSERVATION UNIT

DETAILED DESCRIPTION OF EMBODIMENTS

In this embodiment, an example in which a wireless communicationapparatus, a wireless communication system, and a wireless communicationmethod according to the present invention are applied to a mobilecommunication cellular system such as a cellular phone is represented.Here, a case where, in a wireless communication system in which awireless base station (BS) is a transmission apparatus, and a userequipment (UE) of a mobile station is a receiver apparatus,retransmission control (HARQ) combining propagation path coding using aturbo code and IR-mode retransmission composition is performed will bedescribed as an example. A method of setting an RV parameter, as aretransmission control parameter relating to retransmission control,that represents a start position of retransmission data in the IR modewill be described.

First Embodiment

FIG. 1 is a diagram schematically representing signal transmission in acommunication system according to an embodiment of the presentinvention. A wireless base station 101 that becomes the transmissionapparatus transmits data to a user equipment 102 that becomes thereceiver apparatus. The user equipment 102 replies with Ack(Acknowledgement) or Nack (Negative Acknowledgement) as a responsesignal based on the result of decoding the received data. In a casewhere a Nack response signal is received for first transmission data orretransmission data from the user equipment 102, the wireless basestation 101 performs retransmission by transmitting the nextretransmission data. At this time, the wireless base station 101transmits data at a different start position out of coded data, which isacquired by adding a parity bit to systematic bits, at the time ofretransmission, and thereby acquiring the advantage of retransmissionand composition by employing the IR mode. The wireless base station 101notifies the user equipment 102 of a signal having information thatincludes an MCS and the number of transmissions as a control signal, anRV parameter and the like as a retransmission control parameter. Theuser equipment 102 composes and decodes the retransmission data by usingthe information of the control signal transmitted from the wireless basestation 101.

FIG. 2 is a diagram schematically representing a setting example of theRV parameter according to a first embodiment of the present inventionand shows the image of an IR buffer. In the first embodiment, in a casewhere a retransmission control method is employed in consideration ofadaptive MCS control in which the encoding rate can be changed, as theencoding rate of the first transmission becomes lower, the number ofbits of the RV parameter that is used for signaling is furtherdecreased.

For example, as represented in the setting example of FIG. 1, in a casewhere the encoding rate R is high as R>2/3, the number of bits of the RVparameter is set to two bits. In addition, in a case where the encodingrate R is 1/3<R≦2/3, the number of bits of the RV parameter is set toone bit. In a case where the encoding rate R is low as R≦1/3, the numberof bits of the RV parameter is set to zero bit.

As described above, by setting the number of bits of the RV parameter tobe decreased as the encoding rate of the first transmission isdecreased, the waste of resources for the RV parameter can be preventedfor data having a low encoding rate. In other words, in a case where theencoding rate is low, and the granularity of control of the RV parameteris allowed to be rough, the overhead of the RV parameter signaling canbe lowered. As a result, when adaptive MCS control and retransmissioncontrol are applied, the throughput can be improved by decreasing theoverhead of the retransmission control signaling. Accordingly, theretransmission control can be implemented to have excellentcharacteristics.

Next, concrete configurations of the transmission apparatus and thereceiver apparatus of the wireless communication system according to thefirst embodiment will be described.

FIG. 3 is a block diagram representing the configuration of the majorpart of the transmission apparatus used in the first embodiment of thepresent invention. FIG. 4 is a block diagram representing theconfiguration of the major part of the receiver apparatus used in thefirst embodiment of the present invention.

In this embodiment, a case where the transmission apparatus shown inFIG. 3 and the receiver apparatus shown in FIG. 4 communicate with eachother in a wireless manner by using electric waves is assumed. Forexample, it is assumed that the transmission apparatus shown in FIG. 3is applied to a wireless communication base station apparatus (wirelessbase station; BS) that provides communication services such as mobilecommunications of cellular phones or the like, and the receiverapparatus shown in FIG. 4 is applied to a user equipment (UE) that is awireless communication mobile station apparatus such as a cellular phoneapparatus.

The transmission apparatus shown in FIG. 3 includes: an encoding unit311; a rate matching unit 312; an RV parameter bit-number setting unit313; a control signal generating unit 314; a multiplexing unit 315; atransmission RF unit 316; an antenna 317; a receiver RF unit 318; aseparation unit 319, a demodulating and decoding unit 320; a CRC testunit 321; an Ack/Nack signal demodulating unit 322; a CQI demodulatingunit 323; and a scheduling unit 324.

The electric wave transmitted from a communication counterpart apparatus(for example, the receiver apparatus shown in FIG. 4) is received by theantenna 317. After the high-frequency signal of the electric wavereceived by the antenna 317 is converted into a signal of a relativelylow frequency band such as a base band signal by the receiver RF unit318, the converted signal is input to the separation unit 319. Theseparation unit 319 separates a feedback signal from the receptionsignal and extracts and outputs CQI (Channel Quality Indicator)information, Ack/Nack information, or the like that is included in thefeedback signal. Of the separated feedback signal, the Ack/Nackinformation is input to the Ack/Nack signal demodulating unit 322, andthe CQI information is input to the CQI demodulating unit 323.

The demodulating and decoding unit 320 restores the received data byperforming a demodulating process and a decoding process for thereception signal separated by the separation unit 319. The CRC test unit321 performs an error detection process for a signal after decoding thatis output from the demodulating and decoding unit 320 through CRC(cyclic redundancy check) test, and thereby determining whether or notan error is included in the received data that has been decoded. Then,the received data is output by the CRC test unit 321.

The Ack/Nack signal demodulating unit 322 demodulates the Ack/Nackinformation output from the separation unit 319 and outputs an Ack/Nacksignal, which indicates the result of demodulation of the receptionsignal in the receiver apparatus, to the scheduling unit 324. The CQIdemodulating unit 323 demodulates the CQI information such as SINR(Signal to Interference and Noise Ratio) output from the separation unit319 and outputs a CQI value, which represents the measurement result(reception quality) of the propagation path quality measured in thereceiver apparatus, to the scheduling unit 324. The scheduling unit 324performs a scheduling process based on the Ack/Nack signal output fromthe Ack/Nack signal demodulating unit 322 and a CQI value that is outputfrom the CQI demodulating unit 323 and outputs retransmissioninformation that includes: execution or non-execution of retransmission,the number of transmissions, and the like; the MCS information thatincludes the modulation type of a transmission signal, the encodingrate, and the like; the RV parameter information and the like thatincludes the RV parameter, the number of bits of the RV parameter, andthe like. In addition, various types of information relating to atransmission signal such as the retransmission information, the MCSinformation, and the RV parameter information that are output from thescheduling unit 324 may be referred to as transmission parameters.

The encoding unit 311 performs an encoding process for the transmissiondata and outputs the encoded transmission data to the rate matching unit312. The rate matching unit 312 performs a rate matching process inwhich modulation multiple values and the encoding rate are adaptivelyset and outputs the processed data to the multiplexing unit 315. Here,the encoding unit 311 and the rate matching unit 312 perform an encodingprocess and a rate matching process based on the MCS, the RV parameter,and the like that are output from the scheduling unit 324. In the ratematching unit 312, an IR buffer is disposed. The rate matching unit 312stores the encoded data in the IR buffer, reads out a predeterminedamount of data corresponding to the transmission rate and the encodingrate based on a start position designated by the RV parameter at thetime of retransmission as retransmission data, and outputs theretransmission data. In the receiver apparatus, a retransmissioncomposition process is performed through the IR mode by using theretransmission data and the first transmission data.

The RV parameter bit-number setting unit 313 receives the MCSinformation of the first transmission from the scheduling unit 324 anddetermines the number of bits of the RV parameter based on the encodingrate of the first transmission by using the encoding rate included inthe MCS information. In addition, the RV parameter bit-number settingunit 313 receives the MCS information and the retransmission informationfrom the scheduling unit 324 and sets the RV parameter for anappropriate start position according to the number of transmissionsbased on the determined number of bits of the RV parameter and thenumber of transmissions of the data. The number of bits of the RVparameter and the RV parameter are input to the control signalgenerating unit 314, the encoding unit 311, and the rate matching unit312. A concrete example of the number of bits of the RV parameter andthe setting process of the number of bits of the RV parameter will bedescribed later.

The control signal generating unit 314 generates a control signal thatincludes the RV parameter information as a parameter relating toretransmission control based on the number of bits of the RV parameterand the RV parameter from the RV parameter bit-number setting unit 313and outputs the control signal to the multiplexing unit 315. In thiscontrol signal, the retransmission information, the MCS information, andthe like are also included.

The multiplexing unit 315 performs multiple processing for thetransmission signal including encoded transmission data, the controlsignal including the RV parameter information, and the like. Then, themultiplexing unit 315 generates a transmission signal by performing amodulation process and the like and outputs the transmission signal tothe transmission RF unit 316. In the transmission RF unit 316, afterprocesses such as serial/parallel conversion, an inverse Fouriertransform, and the like are performed for the transmission signal, thetransmission signal is converted into a high frequency signal of apredetermined wireless frequency band. Then, after power amplificationis performed for the transmission signal, the amplified transmissionsignal is transmitted from the antenna 317 as an electric wave. Thetransmission signal transmitted from the transmission apparatus istransmitted to the receiver apparatus as a pilot signal, a controlsignal, a data signal including various types of data, and the like.

In the above-described configuration, the CQI demodulating unit 323implements the function of a propagation path quality acquiring unit. Inaddition, the scheduling unit 324 implements the function of an MCSsetting unit and a retransmission control unit. The RV parameterbit-number setting unit 313 implements the function of a parameterbit-number setting unit and a retransmission control parameter settingunit. In addition, the rate matching unit 312, the multiplexing unit315, and the transmission RF unit 316 implement the function of atransmission processing unit.

On the other hand, the receiver apparatus shown in FIG. 4 includes: anantenna 431; a receiver RF unit 432; a channel estimating unit 433; acontrol signal demodulating unit 434; a demodulating unit 435; adecoding unit 436; an RV parameter identifying unit 437; a first-timeMCS conservation unit 438; a likelihood conservation unit 439; a CRCtest unit 440; an SINR measuring unit 441; a feedback informationgenerating unit 442; an Ack/Nack generating unit 443; an encoding unit444; a multiplexing unit 445, and a transmission RF unit 446.

The electric wave transmitted from a communication counterpart apparatus(for example, the transmission apparatus shown in FIG. 3) is received bythe antenna 431. After being converted into a signal of a relatively lowfrequency band such as a baseband signal by the receiver RF unit 432,the high-frequency signal of the electric wave received by the antenna431 is converted into a reception signal of serial data by performingprocesses such as a Fourier transform and parallel/serial conversion.The output of the receiver RF unit 432 is input to the channelestimating unit 433, the control signal demodulating unit 434, and thedemodulating unit 435.

The channel estimating unit 433 calculates a channel estimation value byperforming channel estimation based on a pilot signal that is includedin the signal transmitted from the transmission antenna of thecommunication counterpart apparatus (transmission apparatus). Thecalculated channel estimation value is input to the demodulating unit315 and the SINR measuring unit 441. The control signal demodulatingunit 434 extracts control information such as the retransmissioninformation including execution or non-execution of retransmission, thenumber of transmissions, and the like, the MCS information including themodulation type, the encoding rate, and the like of a transmissionsignal, the RV parameter information including the RV parameter and thelike by demodulating the control signal transmitted together with thepilot signal. The demodulated control signal is input to thedemodulating unit 435, the RV parameter identifying unit 437, theAck/Nack generating unit 443, and the multiplexing unit 445.

The demodulating unit 435 performs a demodulation process for areception signal corresponding to the receiver apparatus (the receiverapparatus including the demodulating unit) by using the channelestimation value received from the channel estimating unit 433. Then,the demodulating unit 435 performs a deinterleaving process, a ratede-matching process for allowing the modulation multiple values and theencoding rate to match those of the transmission side, and the like andoutputs the reception signal after demodulation to the demodulating unit436. The RV parameter identifying unit 437 outputs the MCS informationof the first transmission that is received from the control signaldemodulating unit 434 as the information on the encoding rate of thefirst transmission to the first-time MCS conservation unit 438 so as tobe stored therein. In addition, the RV parameter identifying unit 437calculates and identifies the number of bits of the RV parameter byusing the encoding rate of the first transmission based on the MCSinformation of the first transmission. Then, the RV parameteridentifying unit 437 demodulates and identifies the RV parameterassigned to the resources of a corresponding number of bits based on thenumber of bits of the RV parameter calculated as above and the RVparameter information output from the control signal demodulating unit434 and outputs the RV parameter to the demodulating unit 436. Thelikelihood conservation unit 439 conserves likelihood information onreception signals received in the past.

The decoding unit 436 restores the reception data by performing adecoding process for the reception signal input from the demodulatingunit 435. At this time, when retransmission is performed, the decodingunit 436 performs a retransmission composition process through the IRmode based on the RV parameter received from the RV parameteridentifying unit 437. In other words, the decoding unit 436 at the timeof retransmission performs a likelihood composition process or the likein which the likelihood information of the past reception signalconserved in the likelihood conservation unit 439 and the likelihoodinformation of the current reception signal are composed together andoutputs the reception data after decoding to the CRC test unit 440. TheCRC test unit 440 performs an error detection process for the signalafter decoding output from the decoding unit 436 through a CRC test andoutputs information on existence of non-existence of data error thatindicates whether an error is included in the reception data afterdecoding to the Ack/Nack generating unit 443. Then, the reception datais output by the CRC test unit 440.

The SINR measuring unit 441 detects the reception state of the pilotsignal based on the channel estimation value estimated by the channelestimating unit 433 and calculates the SINR of the signal transmittedfrom the communication counterpart apparatus (transmission apparatus) asthe measurement result of the propagation path quality. The calculatedSINR is input to the feedback information generating unit 442. This SINRcorresponds to the CQI value that is information representing thepropagation path quality for a desired signal. The feedback informationgenerating unit 442 generates feedback information including the CQIinformation and outputs the feedback information to the multiplexingunit 445.

The Ack/Nack generating unit 443 determines whether or not any error isincluded in the decoded reception data based on the result of errordetection in the CRC test unit 440, generates an Ack/Nack signal, andoutputs the Ack/Nack signal to the multiplexing unit 445. Here, when anyerror is not included in the result of decoding, Ack is generated. Onthe other hand, when an error is included in the result of decoding,Nack is generated.

The decoding unit 444 performs an encoding process for the transmissiondata and outputs the encoded transmission data to the multiplexing unit445. The multiplexing unit 445 performs multiple processing for atransmission signal including the feedback information, the Ack/Nacksignal, and the encoded transmission data, which have been input, andthe like. Then, the multiplexing unit 445 generates a transmissionsignal by performing a rate matching process, in which modulationmultiple values and the encoding rate are adaptively set, a modulationprocess, and the like and outputs the generated transmission signal tothe transmission RF unit 446. In the transmission RF unit 446, afterprocesses such as serial/parallel conversion, an inverse Fouriertransform, and the like are performed for the transmission signal, thetransmission signal is converted into a high frequency signal of apredetermined wireless frequency band. Then, after power amplificationis performed for the transmission signal, the amplified transmissionsignal is transmitted from the antenna 431 as an electric wave. At thistime, the feedback information including the CQI information and aresponse signal for the Ack/Nack signal, which have been transmittedfrom the receiver apparatus, and the like is transmitted to thetransmission device as a feedback signal.

In the above-described configuration, the SINR measuring unit 441 andthe feedback information generating unit 442 implement the function of apropagation path quality notifying unit. In addition, the receiver RFunit 432, the demodulating unit 435, and the control signal demodulatingunit 434 implement the function of a reception processing unit. Thefirst-time MCS conservation unit 438 implements the function of acontrol information storing unit. In addition, the RV parameteridentifying unit 437 implements the function of a retransmission controlparameter demodulating unit.

Next, in this embodiment, the processing sequence for a case where thetransmission apparatus shown in FIG. 3 and the receiver apparatus shownin FIG. 4 communicate with each other will be described below withreference to FIG. 5. FIG. 5 is a sequence diagram representing aconcrete example of the sequence of all the processes relating to thecommunication between the transmission apparatus and the receiverapparatus according to the first embodiment.

Step S1: The transmission apparatus transmits a pilot channel to thereceiver apparatus through the transmission RF unit 316 and the antenna317.

Step S2: The receiver apparatus receives the pilot channel transmittedfrom the transmission apparatus through the antenna 431 and the receiverRF unit 432, performs channel estimation of the propagation path byusing the channel estimating unit 433, and observes the reception stateof the pilot channel. Then, the receiver apparatus measures andcalculates the SINR by using the channel estimation value of the pilotchannel by using the SINR measuring unit 441

Step S3: The receiver apparatus generates feedback information includingthe CQI information according to the SINR calculated as above in thefeedback information generating unit 442 and reports the CQI information(SINR) representing the quality of the propagation path by transmittingthe feedback information to the transmission apparatus through themultiplexing unit 445, the transmission RF unit 446, and the antenna431.

Step S4: The transmission apparatus receives the feedback informationfrom the receiver apparatus through the antenna 317 and the receiver RFunit 318 and demodulates the CQI information by using the separationunit 319 and the CQI demodulating unit 323. Then, the scheduling unit324 sets the MCS including the modulation type, the encoding rate, andthe like based on the CQI information (SINR) of the pilot channel thatis fed back from the receiver apparatus.

Step S5: The transmission apparatus determines the number of bits of theRV parameter based on the MCS set as described above by using the RVparameter bit-number setting unit 313.

Here, the operation of determining the number of bits of the RVparameter in Step S5, which is one of characteristic operations of thetransmission apparatus according to this embodiment, will be describedin detail. The RV parameter bit-number setting unit 313 receives the MCS(the MCS of the first transmission) transmitted toward the communicationcounterpart apparatus (the receiver apparatus) by using the schedulingunit 324 and determines the number of bits of the RV parameter based onthe encoding rate of the first transmission. In addition, the RVparameter bit-number setting unit 313 receives the retransmissioninformation from the scheduling unit 324 and sets the RV parameter foran appropriate start position of data of first transmission according tothe number of transmissions (here, the first transmission). Then, the RVparameter bit-number setting unit 313 outputs the number of the bits ofthe RV parameter and the RV parameter, which have been determined, tothe control signal generating unit 314.

Step S6: The transmission apparatus generates a control signal includingthe RV parameter information based on the number of bits of the RVparameter and the RV parameter determined as above that is output fromthe RV parameter bit-number setting unit 313 by using the control signalgenerating unit 314. In this control signal, the MCS and the informationon the number of transmissions are included.

Step S7: The transmission apparatus generates transmission datadedicated for the use of the corresponding receiver apparatus byperforming processes by using the decoding unit 311, the rate matchingunit 312, and the multiplexing unit 315 based on the MCS set in Step S4.

Step S8: The transmission apparatus transmits the pilot channel, thecontrol signal, and the data signal to the receiver apparatus.

Step S9: The receiver apparatus, similarly to Step S2, measures andcalculates the SINR based on the reception state of the pilot channel byusing the SINR measuring unit 441.

Step S10: The receiver apparatus extracts the MCS information bydemodulating the control signal by using the control signal demodulatingunit 434. Here, the RV parameter identifying unit 437 outputs the MCSinformation of the first transmission to the first-time MCS conservationunit 438 so as to be stored therein.

Step S11: The receiver apparatus performs a reception process byacquiring a channel estimation value of the reception signal by usingthe channel estimating unit 433 and demodulating the reception data, byusing the MCS extracted in Step S10, by using the demodulating unit 435.

Step S12: The receiver apparatus performs an error correction decodingprocess for the reception data, which has been demodulated in Step S11,by using the decoding unit 436.

Step S13: The receiver apparatus performs an error detection process forthe reception data after the error correction decoding of Step S12 byusing the CRC test unit 440.

Step S14: The receiver apparatus generates a corresponding Ack/Nacksignal based on the result of error detection in Step S13 by using theAck/Nack generating unit 443.

Step S15: The receiver apparatus generates the feedback informationincluding the SINR information calculated in Step S9 by using thefeedback information generating unit 442 and reports the SINR and theAck/Nack signal generated in Step S14 to the transmission apparatus in afeedback manner.

Step S16: The transmission apparatus demodulates the Ack/Nack signal,which has been fed back from the receiver apparatus, by using theAck/Nack signal demodulating unit 922.

Step S17: The transmission apparatus determines the start position ofthe retransmission data and sets the RV parameter representing the startposition of the data by using the RV parameter bit-number setting unit313 in a case where the retransmission is performed by detecting Nack inaccordance with the Ack/Nack signal demodulated in Step S16.

Here, the operation of setting the RV parameter in Step S17, which isone of characteristic operations of the transmission apparatus accordingto this embodiment, will be described in detail. First, the schedulingunit 324, in a case where a Nack signal is received, determines that aretransmission is necessary and outputs the MCS of the firsttransmission set by the corresponding receiver apparatus and the numberof transmissions (for example, the second transmission (firstretransmission)) toward the RV parameter bit-number setting unit 313.The RV parameter bit-number setting unit 313 receives the MCS of thefirst transmission and the number of transmissions and sets an RVparameter representing a start position of data for retransmission fortransmitting the remaining data, which has not been transmitted, as muchas is possible based on the number of bits of the RV parameter and thenumber of transmissions of the corresponding data with reference to thenumber of bits of the RV parameter that is based on the encoding rate ofthe first transmission determined in Step S5. Then, the RV parameterbit-number setting unit 313 outputs the set RV parameter to the controlsignal generating unit 314.

Step S18: The transmission apparatus generates a control signalincluding the RV parameter information set as described above, the MCSinformation, and the number of transmissions by using the control signalgenerating unit 314.

Step S19: The transmission apparatus generates transmission data(retransmission data) dedicated for the use of the correspondingreceiver apparatus by performing processes by using the rate matchingunit 312 and the multiplexing unit 315 based on the MCS set in Step S4and the RV parameter set in Step S17.

Step S20: The transmission apparatus transmits the pilot channel, thecontrol signal, and the data signal to the receiver apparatus.

Step S21: The receiver apparatus, similarly to Step S9, measures andcalculates the SINR based on the reception state of the pilot channel byusing the SINR measuring unit 441.

Step S22: The receiver apparatus extracts the MCS information, the RVparameter information, and the number of transmissions by demodulatingthe control signal by using the control signal demodulating unit 434.Then, the RV parameter identifying unit 437 demodulates and identifiesthe RV parameter of this transmission based on the RV parameterinformation.

Here, the operation of identifying the RV parameter in Step S22, whichis one of characteristic operations of the receiver apparatus accordingto this embodiment will be described in detail. The RV parameteridentifying unit 437, first, at the first transmission in theabove-described Step S10, stores the MCS information of the firsttransmission received from the control signal demodulating unit 434 inthe first-time MCS conservation unit 438. Then, the RV parameteridentifying unit 437 receives the number of transmissions from thecontrol signal demodulating unit 434. In the case of a retransmission,the RV parameter identifying unit 437 calculates the number of bits ofthe RV parameter based on the encoding rate of the first transmissionwith reference to the MCS information of the first transmission that isstored in the first-time MCS conservation unit 438. Thereafter, the RVparameter identifying unit 437 demodulates and identifies the RVparameter of this transmission assigned to the resources correspondingto the number of bits based on the number of bits of the RV parametercalculated as described above and outputs the RV parameter to thedecoding unit 436. In addition, the RV parameter identifying unit 437may calculate the number of bits of the RV parameter based on the MCSinformation of the first transmission and conserve the information onthe number of bits of the RV parameter in the first-time MCSconservation unit 438 instead of the MCS information of the firsttransmission.

Step S23: The receiver apparatus performs a reception process byacquiring a channel estimation value of the reception signal by usingthe channel estimating unit 433 and demodulating the reception data(retransmission data), by using the MCS extracted in Step S22, by usingthe demodulating unit 435.

Step S24: The receiver apparatus performs a likelihood compositionprocess corresponding to the RV parameter acquired in Step S22 for thereception data of the first transmission from which an error is detectedin Step S13 by using the reception data of the retransmission by usingthe demodulating unit 436 and the likelihood conservation unit 439. Atthis time, the data of the first transmission and the data of theretransmission are composed by recognizing the data start position foreach transmission based on the RV parameter.

Step S25: The receiver apparatus performs an error correction decodingprocess for the reception data for which the likelihood compositionprocess is performed in Step S24 by using the decoding unit 436.

Step S26: The receiver apparatus performs an error detection process forthe reception data after the error correction decoding of Step S25 byusing the CRC test unit 440. Then, the Ack/Nack generating unit 443generates an Ack/Nack signal in accordance with the result of the errordetection.

Step S27: The receiver apparatus generates the feedback informationincluding the SINR information calculated in Step S21 by using thefeedback information generating unit 442 and reports the SINR and theAck/Nack signal generated in Step S26 to the transmission apparatus in afeedback manner.

Next, a concrete example of setting the number of bits of the RVparameter and the RV parameter according to the first embodiment will bedescribed. FIG. 6 is a diagram representing an example of setting thenumber of bits of the RV parameter corresponding to the encoding rate.FIG. 7 is a diagram representing an example of setting the RV parameter.

In this embodiment, similarly to the setting example represented in FIG.6, in a case where the encoding rate R of the first transmission isgreater than 2/3 (2/3<R), the number of bits of the RV parameter is setto two. In a case where the encoding rate R of the first transmission isgreater than 1/3 and equal to or less than 2/3 (1/3<R≦2/3), the numberof bits of the RV parameter is set to one. On the other hand, in a casewhere the encoding rate R of the first transmission is equal to or lessthan 1/3 (R≦1/3), the number of bits of the RV parameter is set to zero.

For example, in the transmission apparatus, in a case where the encodingrate R of the first transmission is set as R=5/6 in accordance with theCQI information (SINR) that has been fed back from the receiverapparatus, the RV parameter bit-number setting unit 313 uniquely setsthe number of bits of the RV parameter to two bits. FIG. 7 represents anexample of setting of the RV parameter to two bits for a case where theencoding rate R=5/6 in the image of the IR buffer.

At the first transmission, the RV parameter is set as RV=0, and from thebeginning of the encoded data, systematic bits and a part of the paritybits are transmitted. Then, when Nack is received as a result ofdecoding the data of the first transmission, the scheduling unit 324selects and sets as RV=2 so as to transmit the transmission data, whichhas not been transmitted, inside the IR buffer as much as is possiblethrough the second transmission (first retransmission). Thereafter, in acase where when Nack is additionally received as the result of decoding,and third transmission or a transmission thereafter (secondretransmission or a retransmission thereafter) is performed, asdescribed above, in order to transmits the transmission data, which hasnot been transmitted, as much as is possible, the RV parameter issequentially set as RV=1 and 3.

As described above, according to the first embodiment, the MCS is set inaccordance with the result of measurement of the propagation pathquality measured on the reception side, and the number of bits of the RVparameter that is used for controlling the retransmission is set inaccordance with the encoding rate of the first transmission in the MCS.At this time, as the encoding rate of the first transmission isdecreased, the number of bits of the RV parameter is set to bedecreased. Accordingly, in a case where the encoding rate is low, andthe granularity of control of the RV parameter is allowed to be rough,the resources for signaling for notification of the RV parameter isreduced. Therefore, the overhead of the RV parameter signaling can bedecreased. As a result, the waste of resources for controlling theretransmission can be prevented, and accordingly, the throughput can beimproved.

Second Embodiment

FIG. 8 is a diagram schematically representing a setting example of theRV parameter according to a second embodiment of the present inventionand shows the image of an IR buffer. In the second embodiment, aconfiguration example is represented in which a plurality of code wordsis used wherein a code word (CW) represents data series as a controlunit of the MCS. Here, a configuration in which the second embodiment isapplied to a wireless communication system employing MIMO(Multiple-Input Multiple-Output) is represented as an example.

In the second embodiment, in a case where a retransmission controlmethod is employed in consideration of adaptive MCS control in which aplurality of code words is used, as the encoding rate of the firsttransmission becomes lower, the number of bits used for signaling of theRV parameter is further decreased.

For example, as represented in the setting example of FIG. 8, in a casewhere two code words are used, for the first code word (CW 1), themodulation type is 16 QAM. Accordingly, the encoding rate R is high asR=3/4, and thus, the number of bits of the RV parameter is set to twobits. On the other hand, for the second code word (CW 2), the modulationtype is QPSK, and the encoding rate R is low as R=1/2. Thus, the numberof bits of the RV parameter is set to zero bits. Accordingly, for CW 1of which the encoding rate is high and a more flexible setting for theRV parameter is necessary, the number of bits of the RV parameter is setto be large so as to allow the degree of freedom to be high, andflexible retransmission control can be set. In this state, for CW 2,while by setting the number of the bits of the RV parameter is set to besmall as zero, compared to a case where both the code words areconfigured by 2 bit, overhead of the RV parameter signaling of a totalof two bits can be reduced in the entirety of two code words.

As described above, by setting the number of bits of the RV parameter tobe decreased for a code word of which the encoding rate of the firsttransmission becomes lower, the waste of resources for the RV parametercan be prevented for a code word having a low encoding rate. In such acase, while flexible retransmission control can be set for a code wordof which the encoding rate of the first transmission, in which there isa large amount of untransmitted data, is high, the resources for RVparameter signaling in the down bound direction that is used for a codeword on which the influence of a decrease in the degree of freedom ofthe RV parameter is small can be decreased. Accordingly, the overhead ofthe retransmission control signaling for a plurality of code words canbe decreased.

Next, the configurations of concrete examples of the transmissionapparatus and the receiver apparatus of the wireless communicationsystem according to the second embodiment will be described.

FIG. 9 is a block diagram representing the configuration of the majorpart of the transmission apparatus used in the second embodiment of thepresent invention. FIG. 10 is a block diagram representing theconfiguration of the major part of the receiver apparatus used in thesecond embodiment of the present invention.

In the second embodiment, a case where the transmission apparatus shownin FIG. 9 and the receiver apparatus shown in FIG. 10 communicate witheach other in a wireless manner by using electric waves is assumed. Forexample, it is assumed that the transmission apparatus shown in FIG. 9is applied to a wireless communication base station apparatus (wirelessbase station; BS) of the cellular system that provides communicationservices such as mobile communications of cellular phones or the like,and the receiver apparatus shown in FIG. 10 is applied to a userequipment (UE) that is a wireless communication mobile station apparatussuch as a cellular phone apparatus. Here, there is a premise that anMIMO system, which performs wireless transmission and wireless receptionby using a plurality of antennas on both transmission and receptionsides, is configured. In addition, as the form of a communicationsignal, for example, a case where sequential transmission is performedin units of packets by performing communication in a multiple carriercommunication mode by using OFDM (Orthogonal Frequency DivisionMultiplexing) signals or the like is assumed.

The transmission apparatus shown in FIG. 9 includes: an encoding unit911; a rate matching unit 912; an inter-code word RV parameterbit-number adjusting unit 913; a control signal generating unit 914; anMIMO multiplexing unit 915; a plurality of transmission RF units 916 aand 916 b; a plurality of antennas 917 a and 917 b; a receiver RF unit918; a separation unit 919, a demodulating and decoding unit 920; a CRCtest unit 921; an Ack/Nack signal demodulating unit 922; a CQIdemodulating unit 923; a scheduling unit 924; and RV parameterbit-number conservation units 925 for each code word.

The electric wave transmitted from a communication counterpart apparatus(for example, the receiver apparatus shown in FIG. 10) is received bythe antenna 917 b. After the high-frequency signal of the electric wavereceived by the antenna 917 b is converted into a signal of a relativelylow frequency band such as a base band signal by the receiver RF unit918, the converted signal is input to the separation unit 919. Theseparation unit 919 separates a feedback signal from the receptionsignal and extracts and outputs CQI (Channel Quality Indicator)information, Ack/Nack information, and the like of each code wordincluded in the feedback signal. Of the separated feedback signal, theAck/Nack information of each code word is input to the Ack/Nack signaldemodulating unit 922, and the CQI information is input to the CQIdemodulating unit 923.

The demodulating and decoding unit 920 restores the received data byperforming a demodulating process and a decoding process for thereception signal separated by the separation unit 919. The CRC test unit921 performs an error detection process for a signal after decoding thatis output from the demodulating and decoding unit 920 through CRC test,and thereby determining whether or not an error is included in thereceived data that has been decoded. Then, the received data is outputby the CRC test unit 921.

The Ack/Nack signal demodulating unit 922 demodulates the Ack/Nackinformation output from the separation unit 919 and outputs an Ack/Nacksignal, which indicates the result of demodulation of the receptionsignal of each code word in the receiver apparatus, to the schedulingunit 924. The CQI demodulating unit 923 demodulates the CQI informationsuch as SINR output from the separation unit 919 and outputs a CQIvalue, which represents the measurement result (reception quality) ofthe propagation path quality of each code word measured in the receiverapparatus, to the scheduling unit 924. The scheduling unit 924 performsa scheduling process of a plurality of code words based on the Ack/Nacksignal of each code word output from the Ack/Nack signal demodulatingunit 922 and a CQI value of each code word that is output from the CQIdemodulating unit 923 and outputs retransmission information thatincludes: execution or non-execution of retransmission, the number oftransmissions, and the like; the MCS information that includes themodulation type of a transmission signal, an encoding rate, and thelike; the RV parameter information that includes the RV parameter, thenumber of bits of the RV parameter, and the like; and the like astransmission parameters. In addition, the scheduling unit 924, based onthe MCS information and the retransmission information, sets the RVparameter for an appropriate start position in accordance with thenumber of transmissions for each code word based on the number of bitsof the RV parameter determined by the inter-code word RV parameterbit-number adjusting unit 913 and the number of transmissions of thedata.

The encoding unit 911 performs an encoding process for the transmissiondata of a plurality of code words and outputs the encoded transmissiondata to the rate matching unit 912. The rate matching unit 912 performsa rate matching process in which modulation multiple values and theencoding rate are adaptively set and outputs the processed data to theMIMO multiplexing unit 915. Here, the encoding unit 911 and the ratematching unit 912 perform an encoding process and a rate matchingprocess based on the MCS, the RV parameter, and the like that are outputfrom the scheduling unit 924. In the rate matching unit 912, an IRbuffer is disposed for each code word. The rate matching unit 912 storesthe encoded data of a plurality of code words in the IR buffers, readsout a predetermined amount of data corresponding to the transmissionrate and the encoding rate based on a start position designated by theRV parameter at the time of retransmission as retransmission data, andoutputs the retransmission data. In the receiver apparatus, aretransmission composition process is performed for each code wordthrough the IR mode by using the retransmission data and the firsttransmission data.

The inter-code word RV parameter bit-number adjusting unit 913 receivesthe MCS information of the first transmission from the scheduling unit924 and determines the number of bits of the RV parameter by adjustingbetween code words based on the encoding rates of the first transmissionby using the encoding rates included in the MCS information of the codewords. At this time, the inter-code word RV parameter bit-numberadjusting unit 913 sets the number of bits of the RV parameter for eachcode word such that the number of bits of the RV parameter becomessmaller as the code word has a relatively lower encoding rate bycomparing the encoding rates of the first transmission between the codewords while maintaining a total number of the bits of the plurality ofRV parameters to be constant. The set numbers of bits of the RVparameters of the code words are output to the control signal generatingunit 914 and are input to the RV parameter bit-number conservation unit925 for each code word to be stored therein. In addition, the inter-codewords RV parameter bit-number adjusting unit 913 receives the RVparameters from the scheduling unit 924 and outputs the RV parameters tothe control signal generating unit 914.

The control signal generating unit 914 generates a control signal thatincludes the RV parameter information as a parameter relating toretransmission control based on the number of bits of the RV parameterand the RV parameter output from the inter-code word RV parameterbit-number adjusting unit 913 and outputs the control signal to the MIMOmultiplexing unit 915. In this control signal, the retransmissioninformation, the MCS information, and the like are also included.

The MIMO multiplexing unit 915 performs multiple processing for thetransmission signals including encoded transmission data of a pluralityof code words, the control signals including the RV parameterinformation, and the like. Then, the MIMO multiplexing unit 915separates and generates transmission signals to be output to theplurality of antennas by performing a modulation process and the likeand outputs the transmission signals to the transmission RF units 916 aand 916 b. In the transmission RF units 916 a and 916 b, after processessuch as serial/parallel conversion, an inverse Fourier transform, andthe like are performed for the transmission signals, the transmissionsignals are converted into high frequency signals of a predeterminedwireless frequency band. Then, after power amplification is performedfor the transmission signals, the amplified transmission signals aretransmitted from the plurality of independent antennas 917 a and 917 bas electric waves. The transmission signals transmitted from thetransmission apparatus are transmitted to the receiver apparatus aspilot signals, control signals, data signals including various types ofdata, and the like.

In the above-described configuration, the CQI demodulating unit 923implements the function of a propagation path quality acquiring unit. Inaddition, the scheduling unit 924 implements the function of an MCSsetting unit, a retransmission control unit, and a retransmissioncontrol parameter setting unit. The inter-code words RV parameterbit-number adjusting unit 913 implements the function of a parameterbit-number setting unit. In addition, the rate matching unit 912, themultiplexing unit 915, and the transmission RF units 916 a and 916 bimplement the function of a transmission processing unit.

On the other hand, the receiver apparatus shown in FIG. 10 includes: aplurality of antennas 1031 a and 1031 b; a plurality of receiver RFunits 1032 a and 1032 b; a channel estimating unit 1033; a controlsignal demodulating unit 1034; a MIMO demodulating unit 1035; a decodingunit 1036; an RV parameter identifying unit 1037; a first-time MCSconservation unit 1038; a likelihood conservation unit 1039; a CRC testunit 1040; an SINR measuring unit 1041; a feedback informationgenerating unit 1042; an Ack/Nack generating unit 1043; an encoding unit1044; a multiplexing unit 1045, and a transmission RF unit 1046.

The electric waves transmitted from a communication counterpartapparatus (for example, the transmission apparatus shown in FIG. 9) arereceived by the plurality of independent antennas 1031 a and 1031 b.After being converted into a signal of a relatively low frequency bandsuch as a baseband signal by the receiver RF unit 1032 a, thehigh-frequency signal of the electric wave received by the antenna 1031a is converted into a reception signal of serial data by performingprocesses such as a Fourier transform and parallel/serial conversion.Similarly, after being converted into a signal of a relatively lowfrequency band such as a baseband signal by the receiver RF unit 1032 b,the high-frequency signal of the electric wave received by the antenna1031 b is converted into a reception signal of serial data by performingprocesses such as a Fourier transform and parallel/serial conversion.The outputs of the receiver RF units 1032 a and 1032 b are input to thechannel estimating unit 1033, the control signal demodulating unit 1034,and the MIMO demodulating unit 1035.

The channel estimating unit 1033 calculates a channel estimation valueby performing channel estimation based on a pilot signal that isincluded in the signal transmitted from each transmission antenna of thecommunication counterpart apparatus (transmission apparatus). Thecalculated channel estimation values are input to the MIMO demodulatingunit 1035 and the SINR measuring unit 1041. The control signaldemodulating unit 1034 extracts control information such as theretransmission information including execution or non-execution ofretransmission, the number of transmissions, and the like, the MCSinformation including the modulation type, the encoding rate, and thelike of the transmission signal, the RV parameter information includingthe RV parameter and the like by demodulating the control signaltransmitted together with the pilot signal. The demodulated controlsignal is input to the MIMO demodulating unit 1035, the RV parameteridentifying unit 1037, the Ack/Nack generating unit 1043, and themultiplexing unit 1045.

The MIMO demodulating unit 1035 performs a demodulation process for areception signal corresponding to the receiver apparatus (the receiverapparatus including the demodulating unit) by using the channelestimation value received from the channel estimating unit 1033. Then,the MIMO demodulating unit 1035 performs a deinterleaving process, arate de-matching process for allowing the modulation multiple values andthe encoding rate to match those of the transmission side, and the likeand outputs the reception signals of the plurality of code words afterdemodulation to the demodulating unit 1036. The RV parameter identifyingunit 1037 outputs the MCS information of the first transmission that isreceived from the control signal demodulating unit 1034 to thefirst-time MCS conservation unit 1038 so as to be stored therein. Inaddition, the RV parameter identifying unit 1037 calculates the numberof bits of the RV parameter of each code word by using the encoding rateof the first transmission based on the MCS information of the firsttransmission. Then, the RV parameter identifying unit 1037 demodulatesand identifies the RV parameter of each code word assigned to theresources of a corresponding number of bits based on the number of bitsof the RV parameter calculated as above and the RV parameter informationoutput from the control signal demodulating unit 1034 and outputs the RVparameter to the demodulating unit 1036. The likelihood conservationunit 1039 conserves likelihood information on reception signals of thecode words received in the past.

The decoding unit 1036 restores the reception data by performing adecoding process for the reception signal of each code word that isinput from the MIMO demodulating unit 1035. At this time, whenretransmission is performed, the decoding unit 1036 performs aretransmission composition process for each code word through the IRmode based on the RV parameter received from the RV parameteridentifying unit 1037. In other words, the decoding unit 1036 at thetime of retransmission performs a likelihood composition process or thelike in which the likelihood information of the past reception signalconserved in the likelihood conservation unit 1039 and the likelihoodinformation of the current reception signal are composed together andoutputs the reception data of the plurality of code words after decodingto the CRC test unit 1040. The CRC test unit 1040 performs an errordetection process for the signal of each code word after decoding outputfrom the decoding unit 1036 through a CRC test and outputs informationon existence of non-existence of data error that indicates whether anerror is included in the reception data after decoding to the Ack/Nackgenerating unit 1043. Then, the reception data of each code word isoutput by the CRC test unit 440.

The SINR measuring unit 1041 detects the reception state of the pilotsignal based on the channel estimation value estimated by the channelestimating unit 1033 and calculates the SINR of each code word that istransmitted from the communication counterpart apparatus (transmissionapparatus) for each antenna. The calculated SINR of each code word isinput to the feedback information generating unit 1042. This SINRcorresponds to the CQI value that is information representing thepropagation path quality for a desired signal. The feedback informationgenerating unit 1042 generates feedback information including theinformation of each code word and outputs the feedback information tothe multiplexing unit 1045.

The Ack/Nack generating unit 1043 determines whether or not any error isincluded in the decoded reception data based on the result of errordetection of each code word in the CRC test unit 1040, generates anAck/Nack signal for each code word, and outputs the Ack/Nack signal tothe multiplexing unit 1045. Here, when any error is not included in theresult of decoding, Ack is generated. On the other hand, when an erroris included in the result of decoding, Nack is generated.

The encoding unit 1044 performs an encoding process for the transmissiondata and outputs the encoded transmission data to the multiplexing unit1045. The multiplexing unit 1045 performs multiple processing for atransmission signal including the feedback information, the Ack/Nacksignal, and the encoded transmission data, which have been input, andthe like. Then, the multiplexing unit 1045 generates a transmissionsignal by performing a rate matching process, in which modulationmultiple values and the encoding rate are adaptively set, a modulationprocess, and the like and outputs the generated transmission signal tothe transmission RF unit 1046. In the transmission RF unit 1046, afterprocesses such as serial/parallel conversion, an inverse Fouriertransform, and the like are performed for the transmission signal, thetransmission signal is converted into a high frequency signal of apredetermined wireless frequency band. Then, after power amplificationis performed for the transmission signal, the amplified transmissionsignal is transmitted from the antenna 1031 a as an electric wave. Atthis time, the feedback information including the CQI information ofeach code word and a response signal for the Ack/Nack signal, which havebeen transmitted from the receiver apparatus, and the like istransmitted to the transmission device as a feedback signal.

In the above-described configuration, the SINR measuring unit 1041 andthe feedback information generating unit 1042 implement the function ofa propagation path quality notifying unit. In addition, the receiver RFunits 1032 a, 1032 b, the MIMO demodulating unit 1035, and the controlsignal demodulating unit 1034 implement the function of a receptionprocessing unit. The first-time MCS conservation unit 1038 implementsthe function of a control information storing unit. In addition, the RVparameter identifying unit 1037 implements the function of aretransmission control parameter demodulating unit.

Next, the operation of setting the RV parameter for a plurality of codewords, which is one of characteristic operations of the transmissionapparatus according to this embodiment, will be described in detail.

When the numbers of bits of the RV parameters for the plurality of codewords are set, the inter-code word RV parameter bit-number adjustingunit 913 sets the number of bits of the RV parameter for each code wordsuch that the number of bits of the RV parameter becomes smaller as thecode word has relatively lower encoding rate by comparing the encodingrates of the first transmission between the code words while maintaininga total number of the bits of the RV parameters to be constant. Then,the inter-code word RV parameter bit-number adjusting unit 913 outputsthe set value of the number of bits of the RV parameter for each codeword to the RV parameter bit-number conservation unit 925 to be storedtherein.

At the time of retransmission of each code word, the scheduling unit 924sets the RV parameter for the corresponding code word by referring tothe number of bits of the RV parameter that is stored in the RVparameter bit-number conservation unit 925 for each code word. Inaddition, the inter-code word RV parameter bit-number adjusting unit 913may set the RV parameter for each code word. The control signalgenerating unit 914 generates a control signal including the RVparameter information with the number of bits directed by the inter-codeword RV parameter bit-number adjusting unit 913 being used as the base,based on the RV parameter received from the scheduling unit 924 throughthe inter-code word RV parameter bit-number adjusting unit 913.

In addition, the operation of identifying the RV parameters of aplurality of code words, which is one of characteristic operations ofthe receiver apparatus according to this embodiment, will be describedin detail.

The RV parameter identifying unit 1037, at the time of firsttransmission, stores the MCS information of the first transmission ofeach code word that is received from the control signal demodulatingunit 1034 in the first-time MCS conservation unit 1038. Then, the RVparameter identifying unit 1037 receives the number of transmissionsfrom the control signal demodulating unit 1034. Then, in the case ofretransmission, the RV parameter identifying unit 1037 calculates thenumber of bits of the RV parameter of each code word based on theencoding rate of the first transmission by referring to the MCSinformation of the first transmission that is stored in the first-timeMCS conservation unit 1038. Thereafter, the RV parameter identifyingunit 1037 demodulates and identifies the RV parameter of thistransmission for each code word, which is assigned to the resources ofthe corresponding number of bits, based on the number of bits of the RVparameter calculated as described above and outputs the RV parameter tothe decoding unit 1036. Here, the RV parameter identifying unit 1037 maycalculate the number of bits of the RV parameter based on the MCSinformation of the first transmission and conserve the information onthe number of bits of the RV parameter instead of the MCS information ofthe first transmission in the first-time MCS conservation unit 1038.

Next, a concrete example of setting the number of bits of the RVparameter according to the second embodiment will be described. In acase where there are two code words, for example, similarly to theabove-described example of FIG. 8, the total number of the bits of theRV parameter is set to two bits, the number of bits of the RV parameterof a code having a higher encoding rate is set to two bits, and thenumber of bits of the RV parameter of a code having a lower encodingrate is set to zero bits.

FIG. 11 is a diagram representing examples of setting the number of bitsof the RV parameter according to the decoding rate and representsexamples in which there are three code words. Here, the total number ofthe bits of the RV parameter is set to seven bits in both Example 1 andExample 2.

In Example 1, the number of bits of the RV parameter of the first codeword (CW 1) having the highest encoding rate R=0.75 is set to four bits,the number of bits of the RV parameter of the third code word (CW 3)having the second highest encoding rate R=0.50 is set to two bits, andthe number of bits of the RV parameter of the second code word (CW 2)having the lowest encoding rate R=0.33 is set to one bit. In addition,in Example 2, the number of bits of the RV parameter of the first codeword (CW 1) having the highest encoding rate R=0.80 is set to four bits,the number of bits of the RV parameter of the second code word (CW 2)having the second highest encoding rate R=0.75 is set to two bits, andthe number of bits of the RV parameter of the third code word (CW 3)having the lowest encoding rate R=0.50 is set to one bit.

In the above-described example, an example in which the number of bitsof the RV parameter is relatively determined in accordance with theorder of the encoding rates of the code words has been shown as anexample. However, similarly to the first embodiment, after the number ofbits of the RV parameter of each code word is individually set inaccordance with the encoding rate, the numbers of bits of the RVparameters may be adjusted such that a total of the numbers of the bitsof the RV parameters of all the code words is a predetermined number ofbits.

As described above, according to the second embodiment, in the adaptiveMCS control using a plurality of code words, the MCS is set inaccordance with the measurement result of the propagation path qualityof each code word, and the number of bits of the RV parameter of eachcode word for retransmission control is set in accordance with theencoding rate in the MCS of the first transmission. At this time, as theencoding rate of the first transmission become lower, the number of bitsof the RV parameter is set to be smaller. Accordingly, for a code wordhaving a high encoding rate at the first transmission at which there ismuch data that has not been transmitted, a large number of bits of theparameter is assigned, so that flexible retransmission control can beset, and the signaling resource for notification of the RV parameterused for a code word that is not influenced much by lowering the degreeof freedom of the RV parameter is reduced. Accordingly, the overhead ofthe RV parameter signaling of a plurality of code words can bedecreased. As a result, the waste of resources for controlling theretransmission can be prevented in a case where a plurality of codewords is used, and accordingly, the throughput can be improved.

Third Embodiment

FIG. 12 is a diagram schematically representing a setting example of theRV parameter according to a third embodiment of the present inventionand shows the image of an IR buffer. In the third embodiment, aconfiguration example of a case where a plurality of streams (signals)is transmitted for one code word in a case where a plurality of codewords according to the second embodiment is used is represented.

According to the third embodiment, in a case where a retransmissioncontrol method assuming the adaptive MCS control using a plurality ofcode words is employed, the number of bits used for signaling the RVparameter is decreased for a code word having a smaller number ofstreams of the first transmission.

For example, as represented in the setting example of FIG. 12, a casewhere two code words are used, two streams are transmitted in the firstcode word (CW 1) and one stream is transmitted in the second code word(CW 2) is assumed. In such a case, in CW 1, the modulation type is 16QAM, the encoding rate R is R=3/4, and the number of streams is large asbeing two. Accordingly, the number of bits of the RV parameter is set totwo bits. On the other hand, in the CW 2, the modulation type is 16 QAM,the encoding rate R is R=1/2, and the number of streams is small asbeing one. Accordingly, the number of bits of the RV parameter is set tozero bits. Therefore, at the time of retransmission, in CW 2 in whichtwo streams can be transmitted, the number of bits of the RV parameteris decreased. As a result, compared to a case where both the code wordsare set to two bits, the overhead of the RV parameter signaling of atotal of two bits can be reduced in the entirety of the two code words.

As described above, by setting the number of bits of the RV parameter tobe smaller for a code word having a smaller number of streams of thefirst transmission, the resource for the RV parameter can be reduced fora code word that may transmit untransmitted data much more with highpossibility by increasing the number of streams at the time ofretransmission. In such a case, while flexible retransmission controlcan be set for a code word having a large number of streams of the firsttransmission, an increase in the number of streams can be responded, andthe resources for RV parameter signaling in the down bound directionthat is used for a code word on which the influence of a decrease in thedegree of freedom of the RV parameter is small can be decreased.Accordingly, the overhead of the retransmission control signaling for aplurality of code words can be decreased.

Next, the configurations of concrete examples of the transmissionapparatus and the receiver apparatus of the wireless communicationsystem according to the third embodiment will be described.

FIG. 13 is a block diagram representing the configuration of the majorpart of the transmission apparatus used in the third embodiment of thepresent invention. FIG. 14 is a block diagram representing theconfiguration of the major part of the receiver apparatus used in thethird embodiment of present invention.

The third embodiment is an example acquired by modifying a part of thesecond embodiment. In the third embodiment, to a same element as that ofthe second embodiment, a same reference sign is assigned, and detaileddescription thereof is omitted.

In the transmission device shown in FIG. 13, the operations of thescheduling unit 1301, the inter-code word RV parameter bit-numberadjusting unit 1302, and the RV parameter bit-number conservation unit1303 for each code word are different from those of the configurationshown in FIG. 9. The configuration in which the number of bits of the RVparameter is set in accordance with the number of streams of the firsttransmission is used. Here, the operation of setting the RV parameter ina plurality of code words, which is one of characteristic operations ofthe transmission apparatus of this embodiment, will be described indetail.

When the numbers of bits of the RV parameters for the plurality of codewords are set, the inter-code word RV parameter bit-number setting unit1302 sets the number of bits of the RV parameter for each code word suchthat the number of bits of the RV parameter becomes smaller as the codeword has a relatively smaller number of streams by referring to thenumber of streams of the first transmission for each code word, whilemaintaining a total number of the bits of the RV parameters to beconstant. Then, the inter-code word RV parameter bit-number setting unit1302 outputs the set value of the number of bits of the RV parameter foreach code word to the RV parameter bit-number conservation unit 1303 tobe stored therein.

At the time of retransmission of each code word, the scheduling unit1301 sets the RV parameter for the corresponding code word by referringto the number of bits of the RV parameter that is stored in the RVparameter bit-number conservation unit 1303 for each code word. Inaddition, the inter-code word RV parameter bit-number adjusting unit1302 may set the RV parameter for each code word. The control signalgenerating unit 914 generates a control signal including the RVparameter information with the number of bits directed by the inter-codeword RV parameter bit-number adjusting unit 1302 being used as the base,based on the RV parameter received from the scheduling unit 1301 throughthe inter-code word RV parameter bit-number adjusting unit 1302.

In a case where a retransmission occurs in a code word having a smallnumber of streams, the scheduling unit 1301 sets the number of streamsin the transmission parameter such that the number of streams isincreased as the number of retransmissions increases. Accordingly,similarly to the example shown in FIG. 12, in a code word having a smallnumber of streams of the first transmission, even when the bits of theRV parameter are small, by increasing the number of streams at the timeof retransmission while maintaining the modulation type and the encodingrate to be the same, a large amount of data that has not beentransmitted can be transmitted.

In the receiver apparatus shown in FIG. 14, compared to theconfiguration represented in FIG. 10, the operation of the RV parameteridentifying unit 1401 is different, a first-time stream-numberconservation unit 1402 is arranged, and the number of bits of the RVparameter and the RV parameter are configured to be identified inaccordance with the number of streams of the first transmission. Here,the operation of identifying the RV parameters of a plurality of codewords, which is one of characteristic operations of the receiverapparatus according to this embodiment, will be described in detail.

The RV parameter identifying unit 1401, at the time of firsttransmission, extracts the number of streams from the transmissionparameter of the first transmission of each code word that is receivedfrom the control signal demodulating unit 1034 and stores the number ofstreams in the first-time stream-number conservation unit 1402. Then,the RV parameter identifying unit 1401 receives the number oftransmissions from the control signal demodulating unit 1034. In thecase of retransmission, the RV parameter identifying unit 1401calculates the number of bits of the RV parameter of each code wordbased on the number of streams of the first transmission by referring tothe number of streams of the first stream that is stored in thefirst-time stream-number conservation unit 1402. Thereafter, the RVparameter identifying unit 1401 demodulates and identifies the RVparameter of this transmission for each code word, which is assigned tothe resources of the corresponding number of bits, based on the numberof bits of the RV parameter calculated as described above and outputsthe RV parameter to the decoding unit 1036. Here, the RV parameteridentifying unit 1401 may calculate the number of bits of the RVparameter based on the number of streams of the first transmission andconserve the information on the number of bits of the RV parameterinstead of the number of streams of the first transmission in thefirst-time stream-number conservation unit 1402.

In addition, in the above-described setting example, an example in whichthe number of bits of the RV parameter is relatively determined inaccordance with the rank of the number of streams among the code wordsis represented. However, similarly to the first embodiment, after thenumber of bits of the RV parameter of each code word is individually setin accordance with the number of streams, the numbers of bits of the RVparameters may be adjusted such that a total of the numbers of the bitsof the RV parameters of all the code words is a predetermined number ofbits.

As described above, according to the third embodiment, in the adaptiveMCS control using a plurality of code words, the MCS is set inaccordance with the measurement result of the propagation path qualityof each code word, and the number of bits of the RV parameter of eachcode word for retransmission control is set in accordance with thenumber of streams of the first transmission. At this time, for a codeword having a smaller number of streams of the first transmission, thenumber of bits of the RV parameter is set to be smaller. Accordingly,while the retransmission control can be flexibly set for a code wordhaving a large number of streams of the first transmission, thesignaling resource used for the notification of the RV parameter usedfor a code word that may transmit untransmitted data much more with highpossibility by increasing the number of streams at the time ofretransmission can be reduced. In addition, the overhead of the RVparameter signaling of a plurality of code words can be decreased. As aresult, the waste of resources for controlling the retransmission can beprevented in a case where a plurality of code words is used, andaccordingly, the throughput can be improved.

In addition, in the above-described embodiment, the number of bits ofthe RV parameter has been described to zero to two as an example.However, a case where the number of bits is greater than two may be usedas below. In addition, in a case where a plurality of code words isused, examples in which there are two or three code words have beendescribed. However, a case where the number of the code words isincreased or decreased to be four, eight, or the like in accordance withthe number of antennas or the number of beams may be used in a similarmanner.

As described above, the wireless communication apparatus according tothe present invention can be built in a mobile station apparatus(communication terminal apparatus) and a base station apparatus in amobile communication system. Accordingly, a wireless communicationmobile station apparatus, a wireless communication base stationapparatus, and a mobile communication system having the above-describedadvantages can be provided.

The present invention is not limited to the above-described embodiments.Thus, the embodiments may be changed or applied by those skilled in theart based on the description here and known technologies, which is aplan of the present invention. Thus, such a change or applicationbelongs to the scope of the present invention that is requested to beprotected.

In each of the above-described embodiments, a case where the presentinvention is configured by hardware has been described as an example.However, the present invention can be implemented by software.

In addition, each functional block used in the description of each ofthe above-described embodiments is typically realized by an LSI as anintegrated circuit. Such a block may be individually configured as onechip. In addition, a part or all of the functional blocks may beincluded in one chip. Here, the chip is described as an LSI. However, itmay be referred to as an IC, a system LSI, a super LSI, or an ultra LSIdepending on the degree of integration.

In addition, the technique of forming as an integrated circuit is notlimited to the LSI. Thus, such a technique may be implemented by adedicated circuit or a general purpose processor. An FPGA (FieldProgrammable Gate Array) that can be programmed after manufacture as anLSI or a reconfigurable processor in which connections of circuit cellsor settings can be reconfigured may be used.

In addition, when technology of integration circuits that substitutesthe LSI by progress of semiconductor technology or a derivative separatetechnology appear, naturally, the functional blocks may be integrated byusing such technology. There is a possibility that bio technology isapplied thereto.

The present application contains subject matter related to thatdisclosed in Japanese Patent Application 2008-062680 filed in the JapanPatent Office on Mar. 12, 2008, the entire content of which is herebyincorporated by reference.

INDUSTRIAL APPLICABILITY

The present invention has advantages in that the resources used fortransmitting a parameter relating to retransmission control can bereduced, and the throughput can be improved by decreasing the overheadof retransmission control signaling. The present invention is useful asa wireless communication apparatus that can be applied to a wirelesscommunication system such as a cellular system, and more particularly, awireless communication apparatus, a wireless communication system, awireless communication method, and the like that have a retransmissioncontrol function.

The invention claimed is:
 1. A communication apparatus comprising: circuitry which, in operation: sets an MCS (Modulation and Coding Scheme) for data; encodes the data; and sets an RV parameter indicating a start position of transmission data to be transmitted in the data; and a transmitter which, in operation, transmits control information, which includes the MCS and RV information indicating the RV parameter, and the transmission data, wherein: a number of bits of the RV information is set according to a granularity of control; when a number of bits of the RV information is two, the RV parameter is set to any one among 0, 1, 2 and 3; and when a number of bits of the RV information is zero, the control information includes no RV information and the RV parameter is set to
 0. 2. The communication apparatus according to claim 1, wherein the number of bits is set in accordance with an encoding rate of the data.
 3. The communication apparatus according to claim 1, wherein the number of bits is smaller as an encoding rate of the data is lower.
 4. The communication apparatus according to claim 1, wherein the number of bits is set to zero when an encoding rate of the data is equal to or lower than a predetermined value.
 5. The communication apparatus according to claim 1, wherein: the communication apparatus performs communication using a plurality of code words; and the number of bits is set for each of the plurality of code words, and the number of bits is smaller for code word having a lower encoding rate out of the plurality of code words.
 6. The communication apparatus according to claim 5, wherein a total number of bits of the RV information for the plurality of code words is constant.
 7. The communication apparatus according to claim 5, wherein the number of bits of code word having an encoding rate, which is equal to or lower than a predetermined value, out of the plurality of code words is set to zero.
 8. The communication apparatus according to claim 1, wherein: the communication apparatus performs communication using one or a plurality of streams for each of a plurality of code words; and the number of bits is set for each of the plurality of code words, and the number of bits is smaller for code word having a smaller number of streams at a first transmission out of the plurality of code words.
 9. The communication apparatus according to claim 8, wherein a total number of bits of the RV information for the plurality of code words is constant.
 10. The communication apparatus according to claim 8, wherein the number of bits of code word having a number of streams at a first transmission, which is equal to or smaller than a predetermined value, out of the plurality of code words is set to zero.
 11. The communication apparatus according to claim 1, wherein said circuitry, in operation, varies the RV parameter in accordance with a number of retransmissions of the data.
 12. The communication apparatus according to claim 1, wherein the RV parameter is set to 0 at a first transmission.
 13. The communication apparatus according to claim 1, wherein the RV parameter indicates the different start position in accordance with a value of the RV parameter.
 14. The communication apparatus according to claim 1, wherein the start position, which the RV parameter that is 0 indicates, is a position that is closer to a beginning of the data.
 15. The communication apparatus according to claim 1, wherein transmission data, the start position of which the RV parameter that is 0 indicates, has a more number of systematic bits.
 16. A communication method comprising: setting an MCS (Modulation and Coding Scheme) for data; encoding transmission the data; setting an RV (redundancy version) parameter indicating a start position of transmission data to be transmitted in the data; and transmitting control information, which includes the MCS and RV information indicating the RV parameter, and the transmission data, wherein: a number of bits of the RV information is set according to a granularity of control; when a number of bits of the RV information is two, the RV parameter is set to any one among 0, 1, 2 and 3; and when a number of bits of the RV information is zero, the control information includes no RV information and the RV parameter is set to
 0. 